1. Field of the Invention
The present invention relates to a motor and, more particularly, to a motor capable of preventing the deformation of a shaft tube thereof.
2. Description of the Related Art
Modern available motors are mainly categorized as having either a metal or a plastic shaft tube. Referring to FIG. 1, Taiwan Patent Publication No. 384947 discloses a motor having a metal shaft tube. In FIG. 1, a motor 7 comprises a metal shaft tube 71 mounted on a casing seat 72, as well as a stator seat 73 closely fitted to an outer circumferential wall of the metal shaft tube 71. A plurality of bearings 74 is equipped inside the metal shaft tube 71, and a rotor 75 is coupled to the bearings 74.
During assembly, the stator seat 73 generally is fitted to the outer circumferential wall of the metal shaft tube 71 in a close-fitting manner. In a case where the stator seat 73 is fitted to the metal shaft tube 71 too closely, the metal shaft tube 71 will be excessively compressed by the stator seat 73. In this case, the metal shaft tube 71 will be easily deformed due to the compression of the stator seat 73 if there is no buffering between the metal shaft tube 71 and the stator seat 73. In addition, the deformed portions of the metal shaft tube 71 will further compress the bearings 74, causing the bearings 74 to be deformed, damaged or out of position. As a result, the lifespan of the motor 7 is decreased. Also, it is difficult to manufacture and further process the motor 7, and additional manpower will be required to manually mount the metal shaft tube 71 on the casing seat 72, making it costly to produce the motor 7.
Referring to FIG. 2, a motor 8 having a plastic shaft tube is disclosed. The motor 8 mainly comprises a base 81, a stator 82 and a rotor 83. The base 81 has a plastic shaft tube 811 with a bearing 812 fitted therein. The stator 82 is coupled with an outer circumferential wall of the plastic shaft tube 811. The rotor 83 is rotatably coupled with the bearing 812. Based on this, the stator 82 is capable of driving the rotor 83.
The plastic shaft tube 811 of the motor 8 may be integrally manufactured in a manner of injection molding, which is particularly advantageous over the motor 7 in terms of manufacturing, assembly and cost. During assembly, the stator 82 may be fitted to an outer circumferential wall of the plastic shaft tube 811 in a close-fitting manner. In contrast to a metal shaft tube 71 and due to the absence of buffering between the plastic shaft tube 811 and the stator 82, the plastic shaft tube 811 tends to be deformed more easily when the plastic shaft tube 811 is excessively compressed by the stator 82.
To avoid the above potential problems of the motor 8, Taiwan Patent Publication No. 519259 discloses a motor as shown in FIG. 3. In FIG. 3, a traditional motor 9 comprises a shaft seat 91 having an annular groove 911 formed thereon. Based on this, an inner circular wall 912 and an outer circular wall 913 form two opposite sides of the shaft seat 91. The inner circular wall 912 is provided to receive a bearing 92, and the outer circular wall 913 is provided to be fitted by a stator seat 93, with a baffle ring 94 fitted within the annular groove 911. Based on the structure, the deformation of the shaft seat 91 while fitting the stator seat 93 to the shaft seat 91 is avoided, thus preventing the bearing 92 from being excessively compressed by the shaft seat 91. However, molding of the shaft seat 91 is rather difficult as the structure thereof is somewhat complex. Therefore, there is a need to overcome the problem.